The present invention relates to an improved process for the production of 5-nitro-acet-2,4-xylidine.
The compound, 5-amino-acet-2,4-xylidine, is known in the art and is used as an intermediate for the preparation of 5-acetamido-2,4-dimethyl-trifluoromethanesulfonanilide (see, e.g., U.S. Pat. Nos. 3,894,078 and 4,013,444). In general, 5-amino-acet-2,4-xylidine can be produced by catalytically hydrogenating 5-nitro-acet-2,4-xylidine, with the 5-nitro-acet-2,4-xylidine being produced by the nitration of acet-2,4-xylidine. Following nitration, the nitrated mixture is generally added to water. Unfortunately, the 5-nitro-acet-2,4-xylidine is not precipitated in pure form during addition to water, but is in admixture with a substantial amount of the 3-nitro and 6-nitro isomers.
Since the ultimate purpose is to produce a relatively pure 5-amino-acet-2,4-xylidine, the art has taken two separate courses. In the first, the 5-nitro isomer is separated utilizing a relatively complex dissolving and crystallization process using organic solvents. This necessarily creates material and solvent losses. In the currently preferred mode, the nitration mixture is added to water, and the resultant isomer mixture is then hydrogenated. The desired 5-amino-compound is then separated from the hydrogenated mixture, utilizing a relatively complex separation technique.
Various processes are known for the separation of isomers in general. Thus, for example, U.S. Pat. No. 4,246,180 describes a process for separating 1-amino-4-bromoanthraquinone-2-sulfonic acid from the reaction mixture formed by brominating 1-aminoanthraquinone-2-sulfonic acid in sulfuric acid. The process consists of adjusting the sulfuric acid concentration by the addition of the reaction mixture to water or to an aqueous sulfuric acid solution. The adjusted sulfuric acid concentration is described as being from 60 to 85% by weight. Similarly, U.S. Pat. No. 4,235,789 describes a process for separating 1-amino-2-bromo-4-hydroxyanthraquinone from a reaction mixture by adjusting the sulfuric acid content in the mixture to 50 to 80% by weight. Finally, U.S. Pat. No. 3,480,681 describes a process for separating 1,2-dichloro-4-nitrobenzene from an isomeric nitration mixture of the 4-nitro and 3-nitro isomer by adding water to the nitration mixture to dilute the sulfuric acid concentration to 65 to 90% by weight. The desired isomer then selectively, fractionally crystallizes from the nitration mixture. The use of water in separating isomers from nitration mixture is also described in U.S. Pat. Nos. 4,139,558; 3,506,725 and 3,816,551.
One object of the present invention is to provide a simple method for the separation of 5-nitro-acet-2,4-xylidine from a nitration mixture containing, in addition to the 5-nitro isomer, the 3-nitro and 6-nitro isomers. The resultant separated product can then be hydrogenated to produce 5-amino-acet-2,4-xylidine.